Due to the severe environmental impact of exhaust gas emissions of internal combustion engines, the demands with respect to the emission behavior of modern internal combustion engines are becoming ever more stringent. In addition to the reduction of exhaust gas emissions through secondary measures such as, for example, the use of catalytic converters, it is also necessary to markedly reduce the untreated primary pollutant emission produced by the engine.
In this context, the pollutant behavior is influenced considerably, on the one hand, by the normal operation with rapid changes in engine rpm's and changes of the engine load and by the cold engine operation. According to the test cycles for the inspection of engines prescribed by law, the first 60 to 80 seconds of the starting phase of a cold engine are decisive for staying below the exhaust emission limits. Up to 80% of the unburnt hydrocarbons emitted during the entire test cycle are released during this time period at an engine starting temperature of 25.degree.. Cold intake pipe walls and combustion chamber walls, the higher friction loss that must be overcome, and the catalytic converter that has not yet reached operating temperatures and in which the conversion rates in the cold operating state are still very low are only a few of the factors which contribute to a drastic increase in the hydrocarbon emission and the emission of carbon monoxide. At ambient temperatures below 0.degree. C., a further marked increase in the pollutant emission occurs during the cold start and warming-up phases.
A number of options for the reduction of pollutant emissions have already been implemented which largely only become effective, however, when the engine has reached operating temperatures. In addition to structural measures such as, for example, cylinder head and combustion chamber design, position of the spark plugs and of the injection nozzles, number of valves, displacement, stroke-bore ratio, compression ratio, intake port and exhaust port design, the generation of primary pollutants can also be influenced through operative measures. For this purpose, factors lend themselves such as carburetion, ignition moment and injection moment, control times, internal recirculation of residual exhaust gas through control time changes, external recirculation of exhaust gas, cutoff of the fuel supply during the overrun phases, and the use of a phase change material device for the utilization of the "waste heat" of the engine. The hydrocarbon emissions can also be reduced by engine-external measures in the exhaust gas region such as, for example, an after treatment of the exhaust gas through catalytic converter systems, insulation of exhaust manifold and exhaust gas system as well as the use of thermal reactors. The engine-external injection of secondary air during the cold start and warming-up phases promotes the secondary reaction of unburnt hydrocarbons and carbon monoxides in the exhaust gas system and additionally results in a more rapid heating up of the catalytic converter due to the heat released during oxidation. In conventional engines, this takes place by way of an additional secondary air pump which must be driven by an electric motor or by the internal combustion engine itself.